The present invention relates to an electric machine with a closed cooling loop having a gaseous coolant which is subdivided by means of partitions and baffles over at least two heat exchangers, where the cooling gas leaves the outside surface of the stator lamination stack of the machine radially and the two heat exchangers are arranged on the upper and/or lower side of the machine, respectively, perpendicularly to it longitudinal axis.
From DE-AS No. 10 65 074, such an electric machine with a closed cooling loop having a gaseous coolant is known, in which the cooled-down cooling gas approaches the end faces of the stator and the rotor of the electric machine on both sides, mainly axially. The known electric machine has axial canals about the machine shaft as well as radial cooling canals in the stator and the rotor. By means of baffles and partitions, the cooling gas stream is divided over the interior of the machine and the coil head zones at both end faces of the stator and the rotor and are fed to a heat exchanger arranged below the stator lamination stack. The axial length of the heat exchanger is designed so that the heat exchanger extends on both sides beyond the stator lamination stack in the axial direction and covers the respective coil head zones.
For the return of the cooling gas from the heat exchanger, a canal formed by the partitions and the walls of the machine body proper as well as of the housing is provided. In the known electric machine the separation of the sub-streams of the entire cooling gas stream up to the entrance of the cooling gas into the heat exchanger is assured by additional radial partitions. Mixing of the cooling gas sub-streams is possible only after the cooling gas leaves the heat exchanger. For the cooling gas sub-streams conducted over the coil head zones, only parts of the heat exchanger alone are thus available. Thereby, an intensification of the cooling of the cooling gas sub-streams conducted over the coil head zones is achieved.
In the event of a failure or shutdown of the heat exchanger for cleaning purposes, the operation of the machine must be interrupted, however, since the necessary cooling of the cooling gas is no longer assured.
It is further known from DE-AS No. 27 24 422 to permit a very brief failure of a heat exchanger by providing two separate identical heat exchangers which are arranged side by side perpendicularly to the longitudinal axis of the electric machine, so that at least inspection work can be performed during operation. In the case of trouble or for more extensive service work also on only one heat exchanger, it has been necessary heretofore to shut down the machine because one heat exchanger alone can handle only about one-half of the cooling air heated by the machine, and always leaves the other half of the machine uncooled.